6. Define class?
Ans:
A class is a blue print from
which individual objects are created. A class can contain fields and methods to
describe the behaviour of an object.
7. What is JVM?
Ans:
Java Virtual Machine (JVM) :
It is an interpreter for
bytecode. JVM is a platform independent and converts Java byte code into
machine language and executes it. Program calls compiler to translate the
program code into executable code that computer can understand and execute. The
executable code depends upon the computer operating system that we use to
execute our program. It is machine dependent.
8. What is multithreading and
what is the class in which these methods are defined?
Ans:
Multithreading is the mechanism
which allows us to do many things simultaneously. A multithreaded enable us to
executed two or more program at same time which are totally independent of each
other. Each part of such a program is called a thread. Each thread defines a
separate path of execution inside the program. To communicated between two
threads we use methods like wait (), notify () and notifyAll() and these
methods are in Object class.wait().
9. What is the difference between
Process and Thread?
Ans:
The major difference between
threads and processes is:
1) Threads share the address
space of the process that created it whereas processes have their own address.
2) Threads can directly access to
the data segment of its process whereas processes have their own copy of the
data segment of the parent process.
3) Threads communicate directly
with other threads of its process whereas processes use inter-process
communication to communicate with child processes.
4) Threads have almost no
overhead whereas processes have considerable overhead.
5) New threads are easily created
whereas new processes require duplication of the parent process.
6) Threads can exercise
considerable control over threads of the same process; processes can only
exercise control over child processes.
7) Changes to the main thread
affect the behavior of the other threads of the process whereas changes to the
parent process do not affect child processes.
10. How do you declare a class as
private?
Ans:
We can declare a private class as
an inner class.
For example :
class MyPrivateClass
{
private static class MyKey
{
String key = "91234";
}
public static void main(String[] args)
{
System.out.println(new
MyKey().key);//prints 91234
}
}
11. What do you mean by
Constructor?
Ans:
Constructor gets invoked when a
new object is created. Every class has a constructor. If we do not explicitly
write a constructor for a class the java compiler builds a default constructor
for that class.
12. What is data encapsulation
and what’s its significance?
Ans:
Encapsulation is a concept in
Object Oriented Programming for combining properties and methods in a single
unit.
Encapsulation helps programmers
to follow a modular approach for software development as each object has its
own set of methods and variables and serves its functions independent of other
objects. Encapsulation also serves data hiding purpose.
13. What are Loops in Java? What
are three types of loops?
Ans:
Looping is used in programming to
execute a statement or a block of statement repeatedly. There are three types
of loops in Java:
1) For Loops
For loops are used in java to
execute statements repeatedly for a given number of times. For loops are used
when number of times to execute the statements is known to programmer.
2) While Loops
While loop is used when certain
statements need to be executed repeatedly until a condition is fulfilled. In
while loops, condition is checked first before execution of statements.
3) Do While Loops
Do While Loop
is same as While loop with only difference that condition is checked after
execution of block of statements. Hence in case of do while loop, statements
are executed at least once.
14. How garbage collection is done in Java?
Ans:
In java, when an object is not
referenced any more, garbage collection takes place and the object is destroyed
automatically. For automatic garbage collection java calls either System.gc()
method or Runtime.gc() method.
15. What’s difference between
Stack and Queue?
Ans:
Stack and Queue both are used as
placeholder for a collection of data. The primary difference between a stack
and a queue is that stack is based on Last in First out (LIFO) principle while
a queue is based on FIFO (First In First Out) principle.
